Printed circuit board and printing apparatus

ABSTRACT

A printed circuit board includes a front layer including frame ground regions on which connectors to be connected with external apparatuses or communication cables are mounted and which are connected with a ground, a signal ground region which is separated from the frame ground regions at the front layer, on which electronic devices configured to receive signals from the connectors are mounted, and which is connected with a ground, and a static electricity removal ground region separated from the frame ground regions and the signal ground region at the front layer, situated outside the frame ground regions, and connected with a ground.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/983,804, filed on Aug. 3, 2020, which claims priority fromJapanese Patent Application No. 2019-147445 filed Aug. 9, 2019, whichare both hereby incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to printed circuit boards and printingapparatuses.

Description of the Related Art

An electronic device includes a built-in printed circuit board (PCB)fixed to a housing. Passive components, such as a resistor andcapacitor, and active components, such as an integrated circuit (IC) aremounted on the printed circuit board.

In recent years, the sizes of printed circuit boards have been reduceddue to an effect of size reduction of electronic devices. Further,downsizing and high integration of ICs to be mounted on printed circuitboards have been developed in order to reduce power consumption andimprove performance.

As a result of board size reduction, the area of a ground to be areference potential of a printed circuit board is decreased, and itbecomes difficult for noise such as static electricity to escape anddifficult to stabilize a voltage level. Furthermore, as a result ofdownsizing and high integration of ICs, antistatic properties aredecreased, and erroneous operations and damage originating fromdisturbance noise such as static electricity often occur.

Japanese Patent Application Laid-Open No. 2018-117131 discusses acontrol board 5 in which a frame ground region 53 and a signal groundregion 52 are situated with an insulation distance ΔL2 therebetween.

In Japanese Patent Application Laid-Open No. 2018-117131, since theframe ground region 53 and the signal ground region 52 are separated bythe insulation distance ΔL2, signal transmission from the frame groundregion 53 to the signal ground region 52 is prevented. However, it isdifficult to prevent static electricity from entering the frame groundregion 53. For example, in a case where a connector to be connected witha cable or an external apparatus is mounted on the frame ground region53, static electricity charged on the hand of a person holding the cableor the external apparatus, the cable, or the external apparatus entersthe frame ground region 53. In Japanese Patent Application Laid-Open No.2018-117131, signal transmission from the frame ground region 53 to thesignal ground region 52 is prevented, but it is difficult to preventtransmission of all the static electricity. Thus, if an entrance ofstatic electricity to the frame ground region 53 is prevented, anentrance of static electricity to the signal ground region 52 is alsoprevented.

SUMMARY

The present disclosure is to solve the above-described issue and isdirected to a printed circuit board configured to prevent staticelectricity from entering a ground region on which a connector ismounted.

In order to achieve this, a printed circuit board according to thepresent disclosure may comprise a front layer including: a first groundregion on which a connector to be connected with an external apparatusor communication cable is mounted and which is connected with a ground;a second ground region which is separated from the first ground regionat the front layer, on which an electronic device configured to receivea signal from the connector is mounted, and which is connected with aground; and a third ground region separated from the first ground regionand the second ground region at the front layer, situated outside thefirst ground region, and connected with a ground.

Further features of the present disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a configuration of an image forming apparatus.

FIG. 2 is a block diagram illustrating a controller.

FIG. 3 illustrates a printed circuit board in detail.

FIG. 4A is an enlarged view of a portion of a printed circuit board.

FIG. 4B is an enlarged view of another portion of the printed circuitboard.

FIG. 5 is a cross-sectional view along A-A′ specified in FIG. 3 .

FIG. 6 illustrates a static electricity transmission path.

FIG. 7 illustrates a relationship between a resonance frequency of asignal layer and a gain, and a relationship between a resonancefrequency of a ground layer and a gain.

DESCRIPTION OF THE EMBODIMENTS

It should be noted that the following embodiments are merelyillustrative and not intended to limit the scope of the claimedinvention and that not every combination disclosed in the embodiments isalways essential to a technical solution of the present disclosure. Thepresent invention is also not limited to the configurations shown in thedrawings. Each of the embodiments of the present invention describedbelow can be implemented solely or as a combination of a plurality ofthe embodiments. Also, features from different embodiments can becombined where necessary or where the combination of elements orfeatures from individual embodiments in a single embodiment isbeneficial.

First Embodiment

Embodiments of the present disclosure will be described below withreference to the drawings.

<Overall Configuration of an Image Forming Apparatus>

FIG. 1 illustrates a configuration of an image forming apparatusaccording to a first embodiment of the present disclosure. Asillustrated in FIG. 1 , an image forming apparatus 10 includes a scannerunit 12 and a printer unit 13. The scanner unit 12 is an image inputdevice, and the printer unit 13 is an image output device.

The scanner unit 12 is a device configured to read an image formed on adocument and acquire image data. Reflection light of light with which animage formed on a document is irradiated is input to a charge-coupleddevice (CCD) image sensor so that information about the image isconverted into an electric signal. The electric signal is converted intoluminance signals R, G, and B, and the luminance signals R, G, and B areoutput to a controller 11, which will be described below with referenceto FIG. 2 .

Documents set on a tray 1250 of the scanner unit 12 are fed one by oneby a document feeder 1260 to a reading position of an optical unit 1213on a platen glass 1211. Then, each document read by the optical unit1213 is discharged to a sheet discharge tray 1219. Light emitted from alamp 1212 of the optical unit 1213 and reflected by a document is inputto a CCD image sensor 1218 via mirrors 1214, 1215, and 1216 and a lens1217. Regarding the document reading method and alternatively to anautomatic feeding method by the document feeder 1260, a method ofscanning a document on the platen glass 1211 with a carriage on whichthe optical unit 1213 is mounted can be employed. While the imageforming apparatus 10 is configured to perform monochrome printing in thefirst embodiment, it can also be configured to perform color printing.

The printer unit 13 is a device configured to form an image on a sheetusing input image data. While an image forming method of the printerunit 13 according to the present embodiment is an electrophotographicmethod using a photosensitive drum or photosensitive belt, the presentdisclosure is not limited to that method. For example, the printer unit13 may employ an inkjet method in which an ink is discharged from amicro-nozzle array to print an image on a sheet.

The image forming apparatus 10 further includes a plurality of sheetcassettes 1311, 1312, 1313, and 1314 and a manual sheet feeding tray1315. Sheets on which an image is to be formed by the printer unit 13are stored in the plurality of sheet cassettes 1311, 1312, 1313, and1314. A laser driver 1321 of the printer unit 13 drives a laser lightemission unit 1322. The laser driver 1321 emits laser lightcorresponding to image data output from the controller 11 by the laserlight emission unit 1322. The laser light is emitted to a photosensitivedrum 1323, and a latent image corresponding to the laser light is formedon the photosensitive drum 1323. A development device 1324 applies adevelopment agent to the latent image portion of the photosensitive drum1323. A transfer unit 1325 transfers the development agent applied tothe photosensitive drum 1323 to a recording sheet conveyed through asheet conveyance path 1331. The recording sheet with the developmentagent thereon is conveyed to a fixing device 1327 by a sheet conveyancebelt 1326. The fixing device 1327 fixes the development agent to therecording sheet with heat and pressure. The recording sheet conveyedthrough the fixing device 1327 is conveyed through sheet conveyancepaths 1335 and 1334 and is then discharged to a sheet discharge tray1328. In a case where a printed surface is to be reversed and thereversed recording sheet is to be discharged to the sheet discharge tray1328, the recording sheet is guided to sheet conveyance paths 1336 and1338 and thereafter conveyed through a sheet conveyance path 1337 andthe sheet conveyance path 1334.

Further, in a case of two-sided printing, a recording sheet is guidedfrom the fixing device 1327 through the sheet conveyance path 1336 andthen guided to a sheet conveyance path 1333 by a flapper 1329.Thereafter, the recording sheet is conveyed in the reverse direction andguided to the sheet conveyance path 1338 and a re-feed conveyance path1332 by the flapper 1329. The recording sheet guided to the re-feedconveyance path 1332 is conveyed through the sheet conveyance path 1331and fed to the transfer unit 1325.

<Description of a Controller 11 of an Image Forming Apparatus 10>

FIG. 2 is a block diagram illustrating a controller that controls theentire image forming apparatus. The controller 11 configured to controlentire operations of the image forming apparatus 10 will be described indetail below with reference to FIG. 2 .

As illustrated in FIG. 2 , the controller 11 is electrically connectedwith the scanner unit 12, the printer unit 13, and an operation unit 14.The devices of the controller 11 according to the present embodiment aremounted on a single printed circuit board. Alternatively, the devices ofthe controller 11 can separately be mounted on two or more printedcircuit boards. For example, the controller 11 can include a printedcircuit board on which an operation unit interface (operation unit I/F)1105 and a human body detection sensor 1110 are mounted and anotherprinted circuit board on which a central processing unit (CPU) 1101 ismounted. The controller 11 includes the CPU 1101, a random access memory(RAM) 1102, a read-only memory (ROM) 1103, the operation unit I/F 1105,a local area network (LAN) controller 1106, the human body detectionsensor 1110, a sheet detection sensor 1112, and a power control unit1114. The CPU 1101, the RAM 1102, the ROM 1103, the operation unit I/F1105, the LAN controller 1106, the human body detection sensor 1110, thesheet detection sensor 1112, and the power control unit 1114 areconnected with a system bus 1107. The controller 11 further includes ahard disk drive (HDD) 1104, an image processing unit 1109, a scannerinterface (scanner I/F) 1111, and a printer interface (printer I/F)1113. The HDD 1104, the image processing unit 1109, the scanner I/F1111, and the printer I/F 1113 are connected with an image bus 1108.

The CPU 1101 comprehensively controls access to/from each connecteddevice based on a control program stored in the ROM 1103. The CPU 1101also comprehensively controls various types of processing performed bythe controller 11.

The RAM 1102 is a system work memory for the CPU 1101 to operate. TheRAM 1102 is also a memory for temporarily storing image data. The RAM1102 includes a static RAM (SRAM) and a dynamic RAM (DRAM). Data storedon the SRAM is retained even if the power is turned off, whereas datastored on the DRAM is erased when the power is turned off. The ROM 1103stores an apparatus boot program. The HDD 1104 is a hard disk drive andstores a program for controlling the image forming apparatus 10 andimage data.

The operation unit I/F 1105 is an interface unit for connecting thesystem bus 1107 and the operation unit 14. The operation unit I/F 1105receives image data to be displayed on the operation unit 14 from thesystem bus 1107, outputs the received image data to the operation unit14, and outputs information input from the operation unit 14 to thesystem bus 1107.

The LAN controller 1106 controls input and output of information betweenthe image forming apparatus 10 and an external apparatus 50 connectedwith a network 60.

The human body detection sensor 1110 is an infrared sensor array inwhich infrared sensors configured to receive infrared rays are arrangedin matrix. The human body detection sensor 1110 receives infrared raysemitted from a person to thereby detect the person having come near theimage forming apparatus 10. While an example in which the human bodydetection sensor 1110 detects a person is described in the presentembodiment, any objects that emit infrared rays can be detected by thehuman body detection sensor 1110. The human body detection sensor is notlimited to the infrared sensor described above. Any devices other thanan infrared sensor that are sensors (an optical sensor configured todetect light, a distortion sensor configured to be distorted by physicalforce, a magnetic sensor configured to detect magnetism, and atemperature sensor configured to detect temperature) configured todetect an object having come near the image forming apparatus 10 can beemployed.

The sheet detection sensor 1112 detects placement of a sheet on themanual sheet feeding tray 1315.

The power control unit 1114 controls power supply to the components ofthe image forming apparatus 10. Details of the power control unit 1114will be described below.

The image bus 1108 is a transmission path for exchanging image data andis a peripheral component interconnect (PCI) bus, an Institute ofElectrical and Electronics Engineers (IEEE) 1394 bus, or the like.

The image processing unit 1109 performs image processing. The imageprocessing unit 1109 reads image data stored in the RAM 1102 andperforms image processing such as enlargement or reduction, based one.g., Joint Photographic Experts Group (JPEG) or Joint Bi-level ImageExperts Group (JBIG), and color adjustment, on the read image data.

The scanner unit 12 includes a scanner control unit 1201 and a scannerdriving unit 1202. The scanner driving unit 1202 is a device thatincludes a motor for conveying a document set on the tray 1250 to areading position of the scanner unit 12 and physically drives. Thescanner control unit 1201 controls operations of the scanner drivingunit 1202. The scanner control unit 1201 receives setting informationset by a user at the time of performing scanner processing viacommunication with the CPU 1101 and controls the operations of thescanner driving unit 1202 based on the setting information.

The printer unit 13 includes a printer control unit 1301 and a printerdriving unit 1302. The printer driving unit 1302 is a device thatincludes a motor for rotating the photosensitive drum 1323, a motor forrotating the fixing device 1327, and a sheet conveyance motor andphysically drives. The printer control unit 1301 controls operations ofthe printer driving unit 1302. The printer control unit 1301 receivessetting information set by the user at the time of performing printingprocessing via communication with the CPU 1101 and controls theoperations of the printer driving unit 1302 based on the settinginformation.

<Description of a Printed Circuit Board>

FIGS. 3, 4A, and 4B illustrate a printed circuit board in detail. Aprinted circuit board 100 is fixed to a metallic housing 600 withmetallic screws 20 to 24. Integrated circuits (ICs) 200 and 201 aremounted on the printed circuit board 100. The IC 200 is the CPU 1101,and the IC 201 is the LAN controller 1106. Further, connectors 202 and203 are mounted on the printed circuit board 100. An external apparatusand a cable (e.g., universal serial bus (USB) device, USB cable) areconnected to the connector 202, and another external apparatus and cable(e.g., Ethernet router, Ethernet cable) are connected to the connector203. Signals 300, 301, 302, and 303 are transmitted between the IC 200and the connector 202. Signals 304 and 305 are transmitted between theIC 201 and the connector 203. The IC 200 communicates with the externalapparatus via the connector 202. The IC 201 communicates with anexternal apparatus via the connector 203. Each of the signals 300 to 305can be a signal configured to transmit a clock signal, a data signal,supply power, or a signal connected to the ground. In the presentembodiment, the connector 202 is a four-pin (pins 400, 401, 402, and403) connector, and the connector 203 is a two-pin (pins 404 and 405)connector. The numbers of pins of the connectors 202 and 203 are notlimited to four and two.

The IC 200 may be a programmable gate array (PGA) or anapplication-specific integrated circuit (ASIC). The power control unit1114 is a PGA, and the image processing unit 1109 is an ASIC. The ICs200 and 201 are highly integrated, and semiconductor processes of theICs 200 and 201 are in the order of nanometers. The smaller thesemiconductor process is, the lower the antistatic property becomes, sothat the probability of an erroneous operation originating fromexogenous noise such as static electricity increases.

The connector 202 is fixed to the printed circuit board 100 with lockingpins 406 and 407. The connector 203 is fixed to the printed circuitboard 100 with locking pins 408 and 409. In a case where the connector202 is a surface mounted device (SMD) type connector, the locking pins406 and 407 are soldered to a front layer (signal layer 30 shown in FIG.5 ) of the printed circuit board 100. In a case where the connector 202is a dual in-line package (DIP), the locking pins 406 and 407 passthrough the printed circuit board 100 from the front layer (signal layer30) to a rear layer (signal layer 36 shown in FIG. 5 ) of the printedcircuit board 100 and are also soldered to the printed circuit board100. The same applies to the connector 203, so that description thereofis omitted.

The front layer (signal layer 30) of the printed circuit board 100according to the present embodiment includes three ground regionsseparated by slits. The three ground regions are a signal ground region101, a frame ground region 102 (a or b), and a static electricityremoval ground region 103.

The signal ground region 101 is a region on which the ICs 200 and 201configured to receive signals from the connectors 202 and 203 aremounted. The signal ground region 101 is connected with the ground viaan internal ground layer 32. The potential of the internal ground layer32 is a reference potential for the signals 300 to 305 and a referencepotential for the power to be supplied to the ICs 200 and 201. Thesignal ground region 101 is situated outside the frame ground region 102a and the frame ground region 102 b.

The connector 202 is mounted on the frame ground region 102 a, and theframe ground region 102 a is electrically connected with a metal housing600. The frame ground region 102 a is connected with a metallic frame ofthe connector 202.

On the frame ground region 102 b is mounted the connector 203, and theframe ground region 102 b is electrically connected with the metalhousing 600. The frame ground region 102 b is connected with a metallicframe of the connector 203.

In the present embodiment, a static electricity removal ground region103 is provided in addition to the signal ground region 101 and theframe ground regions 102 a and 102 b in the signal layer 30 of theprinted circuit board 100. The static electricity removal ground region103 is in a peripheral portion of the printed circuit board 100.Further, the static electricity removal ground region 103 forms a groundloop without a discontinuity. Further, the static electricity removalground region 103 respectively surrounds the frame ground region 102 awithout a discontinuity, the frame ground region 102 b without adiscontinuity, and in the present embodiment, the signal ground region101 without a discontinuity.

Further, the static electricity removal ground region 103 isrespectively situated at a position that is outside the frame groundregion 102 a and at least corresponds to (in other words faces) aninsertion opening 202 a of the connector 202 into which an externalapparatus or a cable is inserted, and situated at a position that isoutside the frame ground region 102 b and at least corresponds to (inother words faces) an insertion opening 203 a of the connector 203 intowhich a cable is inserted.

The static electricity removal ground region 103 is connected with theground layer 32. The frame ground regions 102 a and 102 b and the signalground region 101 are also connected with the ground layer 32. In otherwords, the static electricity removal ground region 103 is connectedwith the frame ground regions 102 a and 102 b and the signal groundregion 101 at the ground layer 32.

The static electricity removal ground region 103 includes through holesthrough which the screws 20 to 23 are passed. The screws 20 to 23 fixthe printed circuit board 100 to the metal housing 600. The throughholes may be notches. The screws 20 to 23 are metallic screws andconnected with the ground with the printed circuit board 100 fixed tothe metal housing 600.

The static electricity removal ground region 103 is completely separatedfrom the frame ground regions 102 a and 102 b and the signal groundregion 101 in the signal layer 30 by a slit 502. The slit 502 is only inthe signal layer 30 and does not reach the ground layer 32.

The static electricity removal ground region 103 is situated in thesignal layers 30 and 36. The static electricity removal ground region103 of the signal layer 30 and the static electricity removal groundregion 103 of the signal layer 36 are situated in the peripheral portionof the printed circuit board 100. In the present embodiment, the signallayer 36 does not include a frame ground region. Alternatively, thesignal layer 36 can include a frame ground region.

In the present embodiment, the signal ground region 101 is situatedbetween the static electricity removal ground region 103 and the frameground region 102 a, and between the static electricity removal groundregion 103 and the frame ground region 102 b. However, the signal groundregion 101 neither has to be situated between the static electricityremoval ground region 103 and the frame ground region 102 a, nor betweenthe static electricity removal ground region 103 and the frame groundregion 102 b.

The static electricity removal ground region 103 includes a via hole 107and is connected with the ground layer 32.

The slit 502 prevents static electricity having entered the peripheralportion of the printed circuit board 100 from being transmitted to thesignal ground region 101 and the frame ground regions 102 a and 102 b.Static electricity having entered the peripheral portion of the printedcircuit board 100 is transmitted to the metal housing 600 through thevia hole 107 of the static electricity removal ground region 103 and thescrews 20 to 23. Static electricity discharged from a person when adevice or a cable is attached to or removed from the connector 202 or203 is prevented from entering the inside of the static electricityremoval ground region 103. Static electricity discharged near theconnector 202 or 203 is prevented from entering active elements (ICs 200and 201) that are mounted on the printed circuit board 100 and operateat high frequencies.

The frame ground region 102 a is connected with the ground layer 32 andthe static electricity removal ground regions 103 of the signal layer 36via a via hole 106 from the signal layer 30. Static electricitydischarged to the frame of the connector 202 is transmitted to the frameground region 102 a via the locking pins 406 and 407. Then, the staticelectricity is transmitted to the static electricity removal groundregion 103 of the signal layer 36 through the via hole 106 and escapesto the metal housing 600.

Further, the frame ground region 102 a is separated from the signalground region 101 by a slit 500. Further, the frame ground region 102 bis separated from the signal ground region 101 by a slit 501. Further,in the present embodiment, the static electricity removal ground region103 and the frame ground region 102 a are separated by the slits 502 and500. Further, the static electricity removal ground region 103 and theframe ground region 102 b are separated by the slits 502 and 501.Further, the static electricity removal ground region 103 and the signalground region 101 are separated by the slit 502. The term “slit” refersto a groove that physically separates a conductor (e.g. copper film) ofthe signal layer 30 of the printed circuit board 100 so that the signallayer 30 is in an electrically non-conducting state. Specifically, atthe signal layer 30, the signal ground region 101 and the frame ground102 a are separated by the slit 500. Further, at the signal layer 30,the signal ground region 101 and the frame ground 102 b are separated bythe slit 501.

The connector 202 is connected with the ground layer 32 of the printedcircuit board 100 via the via hole 106. The via hole 106 according tothe present embodiment is a through via hole. Similarly, the connector203 is connected with the ground layer 32 of the printed circuit board100 via the via hole 206 (shown in FIG. 4B). A through via hole is athrough hole from a front layer to a rear layer. A through via hole isformed by making a hole from a front layer to a rear layer with a drilland coating the hole with a conductor to connect to a plurality oflayers. The pins 400 to 403 of the connector 202 are connected with theoutside of the frame ground region 102 a, i.e., the signal ground region101, so that the signals 300 to 303 are prevented from being transmittedover two different ground regions. The same applies to the connector203, so that description thereof is omitted.

FIG. 5 is a cross-sectional view illustrating the printed circuit board100 along line A-A′ specified in FIG. 3 . In FIG. 5 , each diagonal-linearea is a ground region (except for the ICs 200 and 202), and eachdotted area is a power layer.

The printed circuit board 100 according to the present embodimentincludes four layers. The number of layers of the printed circuit board100, however, is not limited to four. The printed circuit board 100 mayinclude a different number of layers and for instance six or eightlayers.

The signal layers 30 and 36 are provided to transmit signals output fromthe ICs 200 and 201 to another IC. A signal output from the IC 200 or201 is transmitted to the signal layer 36 in some cases or istransmitted within the signal layer 30 in some other cases.

The signal layer 30 includes signal lines for the signals 300 to 305.The signal layer 30 includes a power supply plane and the ground regions101 to 103 in addition to signal lines for the signals 300 to 305. Theframe ground region 102 a of the signal layer 30 is connected with theground layer 32 and the signal ground region 101 of the signal layer 36via the via hole 106.

The ground layer 32 is to stabilize the voltage level of the ground.

A power layer 34 includes a power supply plane of a plurality of systemsfor use by the ICs 200 and 201 and the connectors 202 and 203. The powersupply plane of the power layer 34 supply power to the ICs mounted onthe signal layer 30 via a via hole 105. Since the potential of the viahole 105 is the same as the potential of the power supply plane, the viahole 105 is not connected with the ground of the signal layer 30, theground layer 32, and the ground of the signal layer 36. The via hole 106is not connected with the power supply plane of the power layer 34.

A material of each layer is a conductor such as copper. Further,prepregs 31 and 35 and a core material 33 are provided between layers.The prepregs 31 and 35 are base materials manufactured by impregnating aglass cloth with a resin such as epoxy and then partially curing theglass cloth. The prepregs 31 and 35 are used to insulate layers when thecopper of the layers and the core materials 33 are layered to form theprinted circuit board 100.

The screw 20 is fixed to the metal housing 600.

When a cable is inserted into or removed from the connector 202 or 203,static electricity may be discharged from a charged human body, acharged device, or the charged cable and may enter the frame of theconnector 202 or 203 that is in contact or the signal lines for thesignals 300 to 305 from the connector 202 or 203.

FIG. 6 illustrates a static electricity transmission path.

When a device or a cable is inserted into or removed from the connector202 or 203, since the physical distance is small, there is a highpossibility that a charged human body or device discharges staticelectricity to the static electricity removal ground region 103 situatedclose to the insertion opening 202 a (shown in FIG. 4A) of the connector202. Static electricity discharged to the static electricity removalground region 103 is transmitted to the ground layer 32 and the signallayer 36 via the via hole 107. Then, the static electricity istransmitted to the metal housing 600 via the screw 20 (path 2000).

Further, static electricity having entered the frame of the connector202 is transmitted to the frame ground region 102 a via the locking pins406 and 407 and is transmitted to the ground layer 32 and the signallayer 36 via the via hole 106. The via hole 106 is connected with thestatic electricity removal ground region 103 of the signal layer 36, sothat the static electricity escapes to the metal housing 600 through thescrew 20 (path 2001).

Noise having entered the signal lines for the signals 300 to 303connected with the connector 202 may reach the IC 200 (path 2002).

There is a path (path 2003) through which static electricity havingentered the static electricity removal ground region 103 and the frameground region 102 a is transmitted to the signal ground region 101 via aparasitic capacitor of the slits 500 and 502. In the present embodiment,the static electricity removal ground region 103 is situated outside theconnector 202 and, furthermore, the two slits 500 and 502 are formed upto the signal ground region 101, so that it is difficult for the staticelectricity to be transmitted to the connector.

As illustrated in FIG. 7 , frequencies at which the signal layer 30 andthe ground layer 32 of the printed circuit board 100 are likely tovibrate differ because while the signal layer 30 includes the threeground regions 101, 102, 103 separated by the slits 500 and 502, theground layer 32 does not include such slits, and the shapes of thesignal layer 30 and the ground layer 32 are significantly different.Even in a case where static electricity transmitted through the path2003 causes a resonance phenomenon at the signal ground region 101 ofthe signal layer 30, a resonance phenomenon of an intensity that is thesame as that at the signal layer 30 is less likely to occur at theground layer 32. Thus, static electricity transmitted to the signallayer 30 is attenuated based on frequency characteristics as the staticelectricity is transmitted to the ground layer 32 and the signal layer36. Therefore, the static electricity is less likely to becomesuperimposed noise as the static electricity is transmitted into theinternal layer.

According to the present embodiment, the static electricity removalground region 103 separated from the signal ground region 101 and theframe ground regions 102 a and 102 b by the slit 502 is situated in theperipheral portion of the printed circuit board 100. Consequently,static electricity is concentrated in the static electricity removalground region 103 in the peripheral portion of the printed circuit board100. Thus, static electricity charged on a person, a cable, or a devicecan escape to the metal housing 600.

Furthermore, since the signal layer 30 of the front layer and the groundlayer 32 of the internal layer have different shapes, the resonancefrequencies are shifted, so that static electricity transmitted to theinternal layer is attenuated. Consequently, antistatic properties of anelectronic device such as a printing apparatus that includes the printedcircuit board 100 built therein improve, and the possibility oferroneous operations of mounted components such as the IC 200 decreases.

Modified Embodiments

While the example in which the printed circuit board according to thepresent disclosure is mounted on the image forming apparatus isdescribed in the above-described embodiment, an apparatus on which theprinted circuit board according to the present disclosure is to bemounted is not limited to an image forming apparatus. For example, theprinted circuit board according to the present disclosure can be mountedon various apparatuses such as notebook personal computers (notebookPCs), tablet PCs, desktop PCs, smartphones, vehicles, air conditioningapparatuses, game machines, and robots.

While the present invention has been described with reference toembodiments, it is to be understood that the invention is not limited tothe disclosed embodiments, but is determined by the scope of thefollowing claims.

What is claimed is:
 1. A printed circuit board comprising a conductorlayer designed on one side of one substrate layer including: a firstground region on which a connector to be connected with an externalapparatus or communication cable is mounted and which is connected witha ground; and a second ground region separated from the first groundregion at the conductor layer, the second ground region being at aposition that is outside the first ground region at least in a regioncorresponding to an opening of the connector on the conductor layer, andconnected with a ground, wherein the opening is an insertion opening ofthe connector into which the external apparatus or the communicationcable are to be inserted.
 2. The printed circuit board according toclaim 1, wherein the second ground region is situated to surround thefirst ground region.
 3. The printed circuit board according to claim 2,wherein the second ground region is situated to surround the firstground region without a discontinuity.
 4. The printed circuit boardaccording to claim 1, wherein the second ground region is situated tosurround an electronic component.
 5. The printed circuit board accordingto claim 4, wherein the second ground region is situated to surround theelectronic component without a discontinuity.
 6. The printed circuitboard according to claim 4, wherein the electronic component isconnected with the connector via a signal line.
 7. The printed circuitboard according to claim 1, wherein the electronic component is an ICchip.
 8. The printed circuit board according to claim 1, wherein theconductor layer further includes a third ground region which isseparated from the first ground region, and the second ground region atthe conductor layer, on which another connector to be connected withanother external apparatus or communication cable is mounted, and whichis connected with a ground.
 9. The printed circuit board according toclaim 1, wherein the printed circuit board is a multi-layer printedcircuit board including at least a signal layer, a power layer, and aground layer.
 10. The printed circuit board according to claim 9,wherein the first ground region and the second ground region areconnected at the ground layer.
 11. The printed circuit board accordingto claim 1, wherein the first ground region is connected with a metallichousing of the connector.
 12. The printed circuit board according toclaim 1, wherein the second ground region includes a hole or notchthrough which a fixing member configured to fix the printed circuitboard to a housing is passed.
 13. The printed circuit board according toclaim 12, wherein the fixing member is a metallic fixing member and thehousing is a metallic housing.
 14. The printed circuit board accordingto claim 1, wherein the printed circuit board is a printed circuit boardof a printing apparatus.
 15. A printing apparatus comprising: a printedcircuit board according to claim 1; and a printing unit configured toprint an image on a sheet.